1. Field of the Invention
The present invention relates to a wobble plate pump.
2. Description of Related Art
Impurities are sometimes removed from water by a reverse osmosis (RO) water purification system. By way of example, a RO unit can be attached to the municipal water supply of a kitchen. The municipal water passes through a reverse osmosis membrane which removes impurities from the water. The pressure drop across the reverse osmosis membrane is relatively high. In some locations the pressure of the municipal water is not great enough to push the water through the RO membrane. For this reason RO units typically have a pump that increases the pressure of the water provided to the reverse osmosis membrane.
FIG. 1 shows a wobble plate pump disclosed in U.S. Pat. No. 4,610,605 issued to Hartley. The Hartley pump has three pistons 1 (only one is shown) that are reciprocated by a wobble plate 2. The wobble plate 2 is typically rotated by the drive shaft 3 of an electric motor (not shown). The piston 1 is attached to a diaphragm 4 which provides an internal seal for the pump.
The piston 1 reciprocates within a pump chamber 5 that is defined by a manifold plate 6. The plate 6 has a one-way inlet valve 7 that allows water to flow into the pump chamber 5 and a one-way outlet valve 8 that allows water to flow out of the pump chamber 5.
The pistons 1 are located symmetrically about the motor drive shaft 3 and swing about a radial arc relative to the drive shaft centerline. The swinging motion of the pistons cause the outer portion of the diaphragm 4 to move a greater distance than the inner portion of the diaphragm 4. The outer portion of the diaphragm will therefore deflect more than the inner diaphragm portion. The unequal diaphragm deflection induces stress in the diaphragm material and decreases the life of the pump. Hartley reduced the diaphragm stress by providing excess material in the outer portions of the diaphragm. It has been found that the excess material can become pinched between the piston and the adjacent housing support element. Diaphragm pinching can be avoided by limiting the travel of the piston. Restricting the travel of the piston reduces the compression ratio of the pump cycle and lowers the output of the pump. It would be desirable to provide a wobble plate pump that minimizes the stresses on the pump diaphragm and maximizes the compression ratio of the pump.
The pistons 1 are attached to a rocker arm 9 by a plurality of screws 10. Having to install screws increases the assembly time and overall cost of producing the pump. Additionally, it has been found that water may leak past the piston/rocker arm interface 11 and into the wobble plate 2. If the electric motor is mounted below the pump, the water may leak into the motor and damage the same. It would be desirable to provide a piston/diaphragm/rocker arm assembly that was relatively inexpensive to assemble and totally seals the wobble plate area of the pump.
As shown in FIG. 2, the pump assembly may be mounted in a vertical position so that the electric motor is located above the pump chamber. Any air that becomes entrapped within the pump chamber 5 will collect in the top of the chamber adjacent to the piston 1. Because the outlet valve 8 is located in the bottom of the pump chamber 5, the air will typically remain in the chamber even during the power stroke of the piston 1. Likewise, when the pump is mounted in a horizontal position, the air will become entrapped in the top of the pump chambers. The entrapped air will cavitate and reduce the output of the pump. It would be desirable to provide a wobble plate pump which evacuates air from the pump chambers when the pump is mounted in either a horizontal portion, or a vertical (motor up) position.
The motor and pump are typically mounted to a wall or base surface by a mounting bracket. AC Power is provided to the motor at a frequency of approximately 50-60 hertz (Hz). This frequency of power can create a resonance in the motor that produces a "humming" sound which reverberates through the mounting bracket and into the wall. The hum can be annoying to the end user. Rubber feet can be placed between the wall and the mounting bracket to dampen the humming sound of the assembly. The rubber feet have been found to dampen only resonant frequencies much lower than 50-60 Hz and are thus ineffective in eliminating the hum of the pump. It would be desirable to provide a mounting bracket that can dampen the resonant audible frequency created by the electric motor.